docs: def unregisterMachine(self, machineName):
          """
          This operation unregisters a portal machine from a portal site. The
          operation can only performed when there are two machines
          participating in a portal site.
          """
          url = self._url + "/machines/unregister"
          params = {
              "f" : "json",
              "machineName" : machineName
          }
          return self._post(url=url,
                            param_dict=params,
                            proxy_url=self._proxy_url,
                            proxy_port=self._proxy_port)